About 10% of the Japanese population suffers from pollinosis developed in springtime such as cedar pollinosis. This condition has been on the increase and is attracting public attention.
The period when pollinosis is developed generally corresponds to the period when pollens scatter. In many cases, symptoms of pollinosis still remain after the season in which cedar pollens scatter because most patients with cedar pollinosis are also sensitized with Japanese cypress pollens (Hiroki cypress pollens) that start to scatter just after the cedar pollen-scattering period. Thus, patients who are also sensitive to Japanese cypress pollens suffer from the symptoms of pollinosis for a significant portion of the year.
Cedar pollens and Japanese cypress pollens possess common antigenicity (Takeshi Ide et al., Allergy Clinic 11, 174-178, 1991). The cross-reactivity of IgE antibodies between cedar pollens and Japanese cypress pollens has been established (Taniai M. et al., Mol. Immunol. 30, 183-189, 1993). The positivity index of patients with spring pollinosis for their allergen-specific IgE antibodies is 83.5% for cedar pollens, 80.0% for Japanese cypress pollens, and 76.4% for both pollens (Mitsuhiro Okano et al., Allergy 43, 1179-1184, 1994). In addition, 60% of the patients with cedar pollinosis possess Japanese cypress pollen-specific IgE antibodies (Yozo Saito, Chiryo (Therapy) 78, 1571-1576, 1996). Based on these reports, it is generally recognized that cedar pollinosis patients can develop pollinosis to Japanese cypress pollens and vice versa.
Pollinosis is a typical immediate type I allergy induced by an antigen-antibody reaction between a pollen allergen (which is an antigen causing allergy and is substantially the same as an antigen) and an IgE antibody specific to the allergen. Thus, pollinosis is now prevented and treated using methods theoretically based on the mechanism by which type I allergies develop. This mechanism is briefly described below.
An antigen that has invaded the body is presented to helper T cells by antigen-presenting cells. As a result, B cells mature into antibody-producing cells. The antibody-producing cells produce an antigen-specific IgE antibody, which binds to the surface of mast cells. A subsequently invading antigen binds to the IgE antibody on the mast cells. This stimulation releases chemical mediators like histamine from the mast cells, thereby causing an allergic symptom.
The following three methods are mainly used to prevent and treat allergies based on the above mechanism: 1) evasion of an antigen that causes allergy, 2) chemotherapy typically using an anti-histaminic, and 3) desensitization therapy using an allergen. However, method 1) is difficult to implement practically, and method 2) is merely symptomatic therapy. Method 3) is expected to be the only treatment attacking the root problem, but it is not always effective and may cause serious side effects such as anaphylactic shock.
For these reasons, peptide-based immunotherapy using T-cell epitope peptides of allergen has been recently attempted to prevent and treat allergies. T-cell epitopes participate in initiating and retaining an immune response to a protein allergen that causes clinical symptoms of allergies. These T-cell epitopes bind to HLA class II molecules on the surface of antigen-presenting cells to stimulate the related T-cell subpopulation. The stimulation is thought to trigger an initial response at the helper T-cell level. This initial response causes proliferation of T cells, secretion of lymphokines, a localized inflammatory response, migration of proliferated immune cells to the inflammatory sites, and activation of the B-cell cascade that precedes antibody production. IgE antibodies that are isotypes of these antibodies are critical to the development and retention of allergies. Furthermore, their production is influenced by the properties of lymphokines secreted by helper T cells at the beginning of the above-described cascade. The T-cell epitope is a basic element or the minimum unit to be recognized by a T-cell receptor. This epitope contains amino acid sequence necessary to recognize the receptor. Allergic inflammation can be treated by controlling the response of the helper T cell, which plays a key role in immunosuppression, using the T-cell epitope peptide.
Known therapeutic agents for allergies using T-cell epitope peptides include a therapeutic composition comprising a T-cell epitope peptide of cat-origin allergen (a PCT application published in Japan (JP-WA) No. Hei 7-505365), a therapeutic composition comprising a T-cell epitope peptide of cedar pollen Cry j 1 (JP-WA-Hei 8-502163), and a multi-epitope peptide obtained by joining T-cell epitopes of cedar pollens Cry j 1 and Cry j 2 (Japanese Patent Application No. Hei 8-80702). The main allergen of Japanese cypress pollen, Cha o 1, is reported to have molecular weights of 45 KD or 50 KD. Each molecule has the same isoelectric point of 6.8 and consists of a protein containing 5% carbohydrate (Takeshi Ide, et al., Nippon Kafun Gakkaishi (Journal of the Japanese Pollen Association) 34, 39, 1988). However, their primary structures were unknown, and accordingly, no T-cell epitope site has been identified on the allergen molecules yet. Recently, the present inventors succeeded in cloning the Japanese cypress pollen allergen gene, and clarified that, in addition to Cha o 1, another type of the allergen, Cha o 2, was present. Furthermore, the primary structures of Cha o 1 and Cha o 2 were determined (Japanese Patent Application No. Hei 6-335089).